Not sure what you’re after but this is how you would get the content of a newly posted comment
add_action( 'comment_post', 'my_comment_callback' );
function my_comment_callback($id) {
$comment = get_comments(array(
'ID' => $id
));
// $content is the actual text the user posted
$content = $comment->comment_content;
}
Is that what you’re looking for?